In my prior U.S. Pat. No. 3,815,362, the contents of which are hereby incorporated by reference, I describe a rotary engine providing two cooperating Stirling cycle systems, which comprises a spherical cavity divided by a pivotable disc into two hemispherical sections, a heated or hot section and a cold section, interconnected by an external conduit. The hot section is divided by a partition into two chambers. A spherical wedge is rotatably mounted in the cold section and is drivingly connected to a crank shaft. Expanding fluids alternating in the heated section cause the disc to pivot and the wedge to rotate and pivot causing rotation of the crank shaft.